Thermal transfer cartridges typically used in dye sublimation printers provide internal locks to prevent the spooled media from unwinding when the cartridge is removed from the printer. The internal locks are disengaged when the cartridge is inserted into the printer, and the cartridge must be positioned to offer desired functional features. Holding or locking the cartridge in position in a thermal printer can be accomplished by latches, over-center spring levers, space gates, or by springs attached to doors.
U.S. Pat. No. 4,718,785 which issued Jan. 12, 1988 to M. J. Spath discloses a thermal printer with a cartridge. The printer is a top loading printer wherein a top portion of the printer is pivotally mounted on a base portion and swings up from the base portion to facilitate insertion of the cartridge. When the cartridge is inserted and the top is closed, the top, acting through springs and other mechanisms, exerts a force on the cartridge to keep the cartridge locked in an operating position. Using such an arrangement requires that the top be opened to replace the cartridge. Accordingly, it would be appreciated that it would be highly desirable to have a thermal printer cartridge which can be inserted and removed easily without having to open the top of the printing unit.
U.S. Pat. No. 4,892,425 which issued Jan. 9, 1990 to Shimizu, et al discloses a front or side loading thermal printer and cartridge. In typical fashion, the cartridge has a supply shaft and a take-up shaft with locking mechanisms to prevent rotation of the supply spool and take-up spool under certain conditions. For example, it is desirable to prevent rotation of the supply spool when the cartridge is being inserted or removed from the printer. The cartridge has tabs on it which fit into grooves or passageways in the body of the thermal printer to aid in the alignment of the cartridge. Alignment is important because the supply and take-up spools must be aligned with the drivers that engage the spools. In front or side loading printers of this sort, the cartridge is held in position by the door which may be spring loaded to assure uniform locking pressure on the cartridge. While the door does an adequate job of locking the cartridge into position during use, there is no way to tell whether the cartridge is properly positioned except to operate the cartridge by making a print. Accordingly, it would be appreciated that it would be highly desirable to have a printer cartridge whose operating position could be checked without having to make a test print.
Many thermal printers rely upon the active force of a door to keep the cartridge in position during use. The doors are typically spring loaded or work in conjunction with springs or other mechanisms to either force the cartridge in a certain position or to maintain the cartridge in a certain position. When the door is opened the force is removed and it is not known whether the cartridge is in the proper operating position. Similarly, there is no way to tell whether the cartridge is in the seated operating position even after the door is closed without a test print. In addition to the time and expense required to make test prints, a spring-loaded door is an elaborate device that requires more time and energy to manufacture, thereby utilizing more natural resources than a simple door. It is desirable to have a cartridge which can be properly positioned in an operating position in a thermal printer without the use of elaborate springs or special doors. It is also desirable to have a cartridge which can be checked for proper positioning without the time and expense of making a test print.